GASTROPODA. 15 
markings and splendid polish, which is produced and preserved by 
two flaps of the mantle, one on each side, which fold over the back, 
a line down the centre of which usually marks where the flaps meet. 
The animals are even more brilliantly coloured than the shells. 
They have no operculum, but a large foot, which they can withdraw 
Fig. 9. 
c 
The Tiger Cowry (Oyprsea tigris). (From the Indo-Pacifie Ocean.) 
a, the shell ; b, the mantle ; c, foot ; d, siphon ; e, proboscis ; /, tentacles ; 
g, eyes. 
entirely within their shell, although the aperture is usually very 
narrow. Cowries, as is well known, are sold as ornaments ; and a 
small yellow species, " the money-cowry " (G. moneta), which is very 
common in the Indian and Pacific Oceans, passes current as coin 
among the negro tribes of certain parts of Africa. The specimen 
of Gyprma leucodon figured on p. 16 is extremely valuable and sup- 
posed to be the only one hitherto discovered. The " orange cowry " 
(Cyprma aurora) is worn by chiefs in the Friendly Islands, and is 
considered the highest order of dignity. Only one small species, 
Trivia europm, is found on the British coast, and about 100 fossil 
forms have been discovered in the Chalk. 
Of the Ovulida, the most curious is the " Weaver's-shuttle " Case 35. 
{Radius volva), in which the shell is peculiarly beaked at both ends. 
It is found living on barked corals (Gorgoniidce), and some of the 
smaller species exhibit differences of coloration, resembling the tints 
of the Gorgonias upon which they are found. 
The Naticas are mostly blind, and have a very large foot, suitable Cases 
for burrowing in the sand when in quest of bivalves. They are very 36 ~37. 
